1. Field of the Invention
The invention generally relates to fiber-reinforced composite conduits or tubes and methods for making such conduits or tubes. More particularly, the invention is related to composite pipe liner for oilfield tubular goods which have improved corrosion resistance, and methods for making such lined tubular goods.
2. Background Art
Oilfield tubular goods are threaded segments or “joints” of seamless pipes made from steel and are used in oil and gas well extraction and injection applications among other applications. Oilfield tubular goods are often exposed to fluids which cause corrosion. It is known in the art to try to control this corrosion by making the tubular joints from corrosion-resistant alloy (“CRA”), such as stainless steels or nickel-based alloys, or by adding corrosion-inhibiting chemicals to the fluid stream, or by lining the exposed inner surfaces of the tubular joints with a corrosion-resistant lining or coating.
Practical corrosion-resistant tubular joint linings known in the art are generally of three types: (1) thin, unreinforced thermoplastic or thermoset plastic coatings, deposited by spraying or other methods on the inner wall of the tube; (2) inserted (such as by pressing) thermoplastic liners; or (3) inserted, fiber-reinforced composite tube liners.
U.S. Pat. No. 4,382,421 issued to Warren et al discloses a typical apparatus for applying a thin (20–23 micrometers), unreinforced epoxy coating to the interior of a tube to prevent corrosion. Thin, unreinforced coatings of this type can have poor durability, particularly when the tubes are handled roughly in transportation or during installation, or when they are used in applications where the fluid flowing through the tube causes erosion, or when tools or instrument are run through the inside of the tubes during service operations.
U.S. Pat. No. 5,306,449 issued Brittain et al, U.S. Pat. No. 5,320,388 issued to Lacy, et al and U.S. Pat. No. 5,861,116 issued to Mandich disclose methods for inserting extruded, rigid, self-supporting thermoplastic tubes as corrosion-resistant liners for oilfield tubular goods. Typical thermoplastic liners, such as high-density polyethylene (“HDPE”) or nylon 11, are limited to working temperatures below about 220 degrees Fahrenheit. So-called engineering thermoplastics, such as those known by their acronyms PVDF, PEEK, or PTFE, which generally have higher working temperatures, generally have been too expensive to be practical as oilfield tubular liners. In order to survive the insertion process, thermoplastic liners are relatively thick (typically about 10–20% of the inner radius of the tube in which they are installed), so they significantly reduce the flow area of the tube in which they are installed. Prior art inserted thermoplastic liners are typically not bonded to the inner diameter of the tube. This means that inserted liners are susceptible to collapse if a vacuum develops inside the tube, or if pressurized fluid in the tube permeates the liner and the internal pressure within the tube is subsequently reduced. Furthermore, unbonded thermoplastic liners cannot be used with threaded tubular end connections fitted with metal-to-metal seals, because these threaded connections require a thin bonded liner which confoms to the movement of the metal-to-metal seal area.
U.S. Pat. No. 3,593,391 issued to Routh discloses an apparatus for lining oilfield tubular goods with a rigid PVC plastic tube, which is then grouted in place inside the oilfield tube with a cement slurry. Lined oilfield tubular goods of this type are available commercially from Rice Engineering, Odessa, Tex. In addition to the grouted PVC liner as described in the Routh '391 patent, there is also available from Rice Engineering fiberglass filament-wound (reinforced) liners for higher-temperature and more-corrosive applications.
Just as is the case for thermoplastic liners, grouted rigid liners of the type described in the Routh '391 patent significantly reduce the internal flow area of the tubes in which they are installed. Furthermore, while thermoplastic liners can be molded around the ends of the tubular joint to seal the ends against corrosion, grouted rigid liners are generally truncated at the end of the tube joint, and are fitted with a seal ring which intrudes into the bore of the tubular joint. Still further, grouted rigid liners are not generally flexible enough to be used successfully with most so-called “premium” oilfield threaded end connections which have integral metal-to-metal seals.
There are also several prior-art methods available to line continuous pipelines, such as sewer pipes or gas distribution lines, with tubular composite liners. One method of sewer-pipe lining is described by U.S. Pat. No. 4,009,063 issued to Wood, which describes a technique for lining a passageway with a resin-impregnated tubular fibrous felt encased in inner and outer impervious linings. This laminated felt tube or “sock” is inserted into a passageway, typically a deteriorated sewer line, and simultaneously inflated and cured-in-place by injected hot water. Techniques of the type described in the Wood '063 patent yield a thick, resin-rich lining with integrated impervious linings, suitable for lining continuous, relatively low-pressure pipelines. They are not particularly suitable for oilfield tubular goods because they can reduce the flow area of the tube joint too much, and there is generally little adhesion to the surrounding pipe. Furthermore, the resin-rich composite lacks the mechanical strength required for oilfield tubular service, and there is no provision for properly terminating the liner at a tube end connection.
U.S. Pat. No. 5,451,351 issued to Blackmore describes a method for rehabilitating sewer pipe which uses a resin-impregnated woven graphite and polyester fiber liner which is expanded into shape by an internal polyurethane bladder. The liner is cured in place by heating resulting from an electrical current passed through the graphite fibers. During the curing process, the composite is bound on its outer layer to the inner wall of the pipe line section, and on its inner surface to the bladder. While this process will yield a relatively thin composite liner, it is not practical for use in lining conductive pipes, such as oilfield tubular goods, because the electrical current used to cure the composite liner will preferentially flow through the steel pipe being lined. Because the polyurethane bladder is left in situ, this method is not particularly suitable for applications exposed to oilfield chemicals. Finally, this process does not provide a means of terminating the liner at a threaded end connection.